Restricted service automatic telephone system



J- WICKS March 13, 1951 RESTRICTED SERVICE AUTOMATIC TELEPHONE SYSTEM Filed June 3, 1947 8 mm. H a I 5 2. 695 T 8 0 I n 22.5 M

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o: oo v .5 538 5 58 W amemzs fl o? no a .5 H 5 53. mm ES 9 SEQ 2528 Attorneys Patented Mar. 13, 1951 RESTRICTED SERVICE AUTOMATIC TELEPHONE SYSTEM John Wicks, Biloxi, Miss., assignor to Automatic Electric Laboratories, 1110,, Chicago, 111., a corporation of Delaware Application June 3, 1947, Serial No. 752,055

8 Claims.

The present invention relates to automatic telephone systems and more particularly to such systems in which different groups of subscriber substations are rendered corresponding difierent classes of service.

In an automatic telephone system serving a central ofiice area and the adjacent suburban areas, calls from the subscriber substations in the central ofllce area that are to be completed to subscriber substations in the suburban areas are usually first extended to an operator switchboard in the central office area and then routed by the operators thereat to the subscriber substations in the suburban areas. While this system is entirely satisfactory in operation, a large switchboard in the central office, staffed by a great number of operators, is required in order to complete the calls from the central office area to the suburban areas.

Accordingly, it is an object of the present in? vention to provide an automatic telephone system comprising an improved switching arrangement; whereby subscriber substations of a first class in the central ofiice are rendered a corresponding class of service permitting them to set up connections to subscriber substation in .the suburban areas, and subscriber substations of a second class in the central office are rendered a corresponding class of service preventing them from setting up connections to subscriber sub.- stations in the suburban areas.

Another object of the invention is to provide an automatic telephone system of the character described; wherein the first and second classes of service mentioned are rendered to the corresponding classes of subscriber substations regardless of whether the subscriber substations ar connected to individual or party lines.

Another object of the invention is to provide an automatic telephone system of the character described that includes subscriber substations of first and second classes that are connected to the same party lin and rendered corresponding first and second classes of service.

A further object of the invention is to provide .an automatic telephone system in which different classes of service are rendered tosubscriber substations; wherein the classes of service are selectively established by an improved arrangement including apparatus provided at the subscriber substations.

A further object of the invention is to provide an automatic telephone system in which different classes of service are rendered o sub criber substations; wherein the classes .of service are selectrunk call.

tively established by an improved arrangement including different types of digit transmitting mechanism provided at the subscriber substations.

A still further object of the invention is to provide in a telephone system including a first exchange provided with subscriber substations of firs-t and second classes and automatic switching apparatus accessible thereto; an improved arrangement whereby the switching apparatus is controlled when a trunk call is initiated to select an idle trunk extending to another exchange, and whereby the switching apparatus is reopere ated to release the selected trunk and to route the call to an interceptor operator position in the event a subsequent control performed at the calls ing subscriber substation indicates that it is of the second class that is not entitled to make such a Further features of the invention pertain to the particular arrangement .of the circuit ele= merits .of the system whereby the above outlined and additional operating features thereof are attained.

The invention both as to its or anization and method of Operation, together with further ob j-ects and advantages thereof, will best be understood by reference to the f llowin sp fic o taken in connection with the accompanying drawing in which the single figure illustrates the details of an automatic telephone system having incorporated ther in the features o he p e n invention. I

Referring now more particularly to the drawing, there is illustrated an automatic telephone system comprising a central ofli ce Ill and a remote exchange 29. The central office it is connected to the remote exchange as by a group of seven trunk lines, including the trunk line B I.

The central ofiice It! may serve a group of sev eral hundred subscriber lines, rendered twoindividual classes of service includin non-restricted service and restricted service; and comprising both private or individual lines and party lines. A first group of these subscriber lines includes the partly line 38 having the subscriber substations Ti and T2 connected thereto, and respectively rendered non-restricted and restricted services. Each subscriber substation rendered non-restricted service is provided with conventional substation apparatus; while each subscriber substation rendered restrictive service is provided with substation apparatus including a unique dial or digit transmitting mechanism. For example, the subscriber substation Tl rendered non-restricted service is provided with substation apparatus including a telephone instrument H, a hook-switch |2, and a dial l3; the dial l3 including a pair of impulsing springs M and a pair of off-normal springs l5. Similarly the subscriber substation T2 rendered restricted service is provided with substation apparatus including a telephone instrument 2|, a hook switch 22, and a dial 23; the dial 23 including a pair of impulsing springs 24 and a pair of ofi-normal springs 25, one of which is connected to ground potential at the subscriber substation T2. Each subscriber line is provided with a line circuit individual thereto; the line circuit 35 being individual to the party line 30. Further, the central ofiice I comprises a plurality of groups of links each serving a group of one-hundred of the subscriber lines; the first group of links, including the link 5|, serves the first group of one-hundred subscriber lines, including the party line 30 extending to the subscriber substations TI and T2. The first group of links, including the link 5|, is provided with an associated distributor 40 individual thereto; and each link comprises a finder and a, selector, the link 5| comprising the finder 52 and the selector 53. Also the central oifice In comprises a plurality of groups of connectors each serving a group of one-hundred of the subscriber lines; the first group of connectors, including the connector 6 l, serves the first group of one-hundred subscriber lines, including the party line 30 extendin to the subscriber substations TI and T2.

Also the central office In comprises a group of trunk circuits terminating the trunk lines in the group extending to the remote exchange 20, the trunk circuit 82 terminating the trunk line 8|; and an interceptor operator position 95. The interceptor operator position 95 terminates a group of three trunks, including the trunk 92, terminated by another group of trunk circuits, including the trunk circuit 9|, the trunk 92 being terminated by the trunk circuit 9|. Also, the central oifice |0 comprises a group of secondary trunks, including the secondary trunk I00. Each of the secondary trunks in the group, including the secondary trunk H30, is provided with an incoming trunk accessible to the selectors of the links in the different groups, the secondary trunk I00 bein provided with the incoming trunk ||0 accessible to the selector 53 of the link 5| in the first group. Each of the trunk circuits in the group, including the trunk circuit 82, is provided with an incoming trunk accessible to the hunt switches incorporated in the secondary trunks I00, etc.; the trunk circuit 82 being provided with the incoming trunk 84 accessible to the hunt switch I90 incorporated in the secondary trunk H10. Each of the trunk circuits in the group, including the trunk circuit 9|, is provided with an incoming trunk accessible to the hunt switches incorporated in the secondary trunks I00, etc; the trunk circuit 9| being provided with the incoming trunk as accessible to the hunt switch |00 incorporated in the secondary trunk I00.

The remote exchange 20 serves a group of subscriber substations, including the subscriber substation T3; and comprises automatic switching apparatus 83 of the Strowger type terminating the trunk lines 8|, etc., and having access to the subscriber lines 85, etc., respectively extending to the subscriber substation T3, etc. Also the switching apparatus 83 is accessible to the subscriber substation T3, etc. via the subscriber lines 85. etc.

Preferably in the central office l0, each of the links is identical to the link 5| which comprises the finder 52 and the selector 53, of the Strowger types. Thefinder 52 has access to the first group of one-hundred subscriber lines, including the party line 30; while the selector 53 has access to the different groups of connectors, including the connector 6| in the first group; and also access to the group of secondary trunks I00, etc. The connector 6| is accessible to the selector 53 by way of the associated incoming trunk I; and the secondary trunk I00 is accessible to the selector 53 by Way of the associated incoming trunk ||0.

Preferably, each of the secondary trunks is identical to the secondary trunk H10; which comprises a relay group, including an answer relay R|20, a detector relay RI30, a line relay RIM], a hold relay R450, a dial relay EH50, an intercept relay EHO and a test relay RIBB; as well as the hunt switch we. The hunt switch is of the rotary type, including four wipers |9| to 494, inclusively, provided with individually associated contact banks, and a magnet M| for driving the wipers noted step by step in the clockwise direction.

A better understanding of the connection and arrangement of the telephone system will be facilitated from the following description of the operation of the apparatus incorporated therein incident to the extension of various connections from the subscriber substations in the central ofiice 50.

Local calls in the central ojfice 10 First assuming that a call is initiated at any subscriber substation in the central ofiice i0, such, for example as the subscriber substation Tl, rendered non-restricted service; when the call is initiated at the subscriber substation T! by the removal of the telephone instrument thereat from its associated switch hook, the hookswitch I2 is closed, completing an obvious connection including the impulsing springs M of the dial l3, across the line conductors C3| and C32 ofthe party line 30. The line circuit 35 is controlled over the party line 30 to apply ground potential to the start conductor C38 extending to the associated distributor 45; whereby the distributor Bil operates in order to assign an idle one of the links in the first group to the calling party line 35, such, for example, as the link 5|. Also the line circuit 35 marks, by the application of battery potential upon the control conductor C33 of the party line 82, the position thereof before the finder 52; and marks, by the application oi ground potential to the control conductor C35, the party line 30 as busy to the connectors in the first group including the connector 6| having access thereto. The finder 52 of the link 5! is controlled by the distributor 40 to find the party line 30; whereupon the subscriber at the calling subscriber substation T| receives dial tone, and then proceeds to,dial the first digit of the directory number of the called subscriber substation. The selector 53 responds to the first digit mentioned to select the indicated group of connectors and then an idle connector therein. For example, the selector 53 may select the particular connector 0| by way of the associated incoming trunk 1|; whereby the operation of the connector BI is placed under the control of the subscriber at the calling subscriber substation T|. The subscriber at the calling subscriber substation T| then proceeds to dial the second 75 and third digits of the directory number of the called subscriber substation; whereby the connector BI operates to select the subscriber line extending to the called subscriber substation and proceeds to test the idle or busy condition thereof; all in a conventional manner. Further operation of the connector is entirely conventional; and subsequently the release of the established connection to the called subscriber substation is brought about when the subscriber at the calling subscriber substation TI replaces the receiver of the telephone instrument I I upon its associated switch hook.

In passing it is noted that each time the subscriber at the calling subscriber substation TI operates the dial I3, the oiT-normal switch springs I therein are actuated into engagement, thereby to complete a path for short-circuiting the tele phone instrument II in a conventional manner. When the finger wheel of the dial I3 is then released, the impulsing springs It thereof, operate to transmit over the party line 30 the impulses of the corresponding digit; and when all of the impulses of the digit have been transmitted, the set of off normal springs I5 in the dial I3 are again actuated into open-circuit relation, interrupting the previously mentioned path for short-circuiting the telephone instrument I I, in a conventional manner. It is noted that the set of ofi-normal springs I5 includes the spring I 6 which is connected to no-potential, whereby no unique control is brought about over the party line 35 incident to operation of the dial I3.

In view of the foregoing description of the extension of a local call from the subscriber substation TI rendered non-restricted service, it will be understood that a local call is initiated and extended in an identical manner from a subscriber substation rendered restricted service, such for example, as the subscriber substation T2. In passing it is noted that each time the dial 23 at the calling subscriber substation T2 is operated, the oil-normal springs 25 therein are actuated into engagement, thereby to complete a path for short-circuiting the telephone instrument 2|, in a conventional manner. Also, each time the set of off-normal springs 25 is thus operated, the spring 26 connected to ground potential is included in the path mentioned; whereby ground potential is applied to both of the line conductors CSI and C32 of the party line 3. the line conductors mentioned of the party line 39 has no effect in the associated selector 53, etc., and in the connected connector 6|, etc. Accordingly, the selector 53, etc. and the connector GI, etc. respond to the appropriate digits dialed at the calling subscriber substation T2 in order to extend the local call to the called subscriber substation in the manner previously explained.

Trunk calls from the central office to the remot exchange First assume that a call has been initiated {at the subscriber substation 'I'I rendered non-restricted service in the central ofice I5; that the finder 52 of the link '5I has operated to find the party line extending to the subscriber substation TI; that the selector 53 of the link 51 is conditioned to be responsive to the fi-rst dig it dialed at the calling subscriber substation TI; and that the call is to be extended to a ca lle'cl subscriber substation, such for example, as the subscriber substation T3 in the remote exchange 2%. The subscriber at the calling subscriber substation TI proceeds to dial the first digit of the .idirectory This application of ground potential to o 6. number of the called subscriber substation T3 in the remote exchange 20; thereby to caus operation of the selector 53 in order to select an idle secondary trunk in the associated group. For example, the selector 53 may select the trunk I I0 extending to the secondary trunk I00, the trunk I I 0 being marked as idle thereto by the application of battery potential by way of the lower winding of the answer relay RIZII to the control conductor CI I3 of the trunk III]. When the selector 53 seizes the trunk IIII, the loop circuit from the calling subscriber substation TI is extended to the line conductors CIII and CI I2 :of the trunk I I I3 and by way of the contacts I2I and I24, the upper and lower windings of the detector relay RI3II, the winding of the line relay RIM! and the impedance element I respectively to battery and ground potentials. When this loop circuit is thus completed the line relay RI operates; however, the detector relay RI 39 does not operate as of the differential type. Upon operating, the line relay RM?) completes, at the contacts I42, an obvious circuit for operating the hold relay RIEEI. Upon operating the hold relay RI'56 completes, at the contacts I52, an obvious path for applying ground potential to the control conductor CI I3 of the trunk IIIl, thereby to retain the link 5i in its operated position and to marl; the trunk I II] as busy to the other selectors having access thereto.

Also the hold relay BI completes, at the contacts I53, a path, including th contacts I96, I84 and I13, for applying battery potential by way of the magnet Mill-5 Of the hunt switch I to the wiper I93 thereof. The wipers noted of the hunt switch I9 occupy their last operated position at this time; and assuming that the wipers noted of the hunt switch I occupy the positions illustrated, ground potential appears upon the wiper I93 by virtue of the grounded condition of the engaged contact in the associated contact bank. Accordingly the magnet MISS operates to interrupt, at the contacts I96, the above traced operating circuit therefor. The magnet M'I95 then restores in order to recomplete, at the contacts I95, the previously traced path for applying battery potential by way of the magnet MI95 to the wiper I93. Also upon operating and then restoring, the magnet Mist drives the wipers noted of the hunt switch I90 an additional step in the clockwise direction; whereby the wiper I 93 en ages the contact in the associated contact bank terminating the control conductor of the first trunk line extending between the central ofiice III and the remote exchange 20. Further operation of the magnet MI95 depends upon the idle or busy condition of the first trunk line mentioned extending between the central office I0 and the remote exchange 29; and assuming that all of the trunk lines extending between the central ofiice I0 and the remote exchange 20 and preced ng the trunk line 3| are busy at this time, the magnet M I 95 operates buzzer-fashion in order to drive the wipers noted of the hunt switch I90 step by step in the clockwise direction and into engagement with the contacts in the associated contact banks terminating the incoming trunk 84 etxending to the trunk circuit 82 that, in turn, terminates the trunk line BI extending between the central oifice Ill and the remote exchange (28.

When the wipers noted of the hunt switch I90 engage the contacts in the associated contact banks terminating the incoming trunk 84, further operation of the hunt switch I90 is arrested 75 since battery potential in the trunk circuit 2 is applied to the control conductor of the incoming trunk 84 and consequently to the wiper 193 of the hunt switch 199, completing a path substantially identical to that previously traced for short-circuiting the magnet M195. Also at this time, a circuit, including the contacts 152, 132 and 195, is completed for energizing the winding of the test relay 188 in series with the magnet Mi95; whereby the test relay R180 operates shortly thereafter, it being of the slow-to-operate type. However, the magnet M195 does not operate due to the high series resistance of the winding of the test relay R18ii. Upon operating, the test relay R120 interrupts, at the contacts 184, the previously traced connection between the magnet M195 and the Wiper 193 of the hunt switch 199; and completes, at the contacts 183, a path, includingthe contacts 152 and 1'13, for applying direct ground potential to the wiper 1913, and consequently to the control conductor of the incoming trunk 8 Also the test relay R188 completes, at the contacts 181 and i82, a path including the contacts 152 and 1H for bridging the uppe winding of the answer relay R126 across the line wipers 191 and. 192 of the hunt switch 190, and consequently across the line conductors of the incoming trunk 8 1; whereby the trunk circuit 82 is seized. Also the application of ground potential upon the control conductor oi the incoming trunk 15 5 is efiective to mark the trunk line 81 as busy to the hunt switches in the other secondary trunks having access thereto. When the above traced loop circuit between the upper winding of the answer relay R128 and the trunk circuit 82 is thus completed, the answer relay REZQ does not operate since it is poled to operate incident to the reversal of potential over the loop circuit mentioned as explained more fully hereinafter. Accordingly at this time, the hunt switch 1913 incorporated in the secondary trunk 1118 has operated automatically to seize the idle incoming trunk 84 extending to the trunk circuit 82, terminating the trunk line 81 extending between the central office 10 and the remote exchange 25, when the selector 53 operated to seize the incoming trunk 1113 extending to the secondary trunk 1153. Also at this time, the trunk circuit 82 operates to control over the trunk line 81 the switching apparatus 83 in the remote exchange 29; whereby the sw' ching apparatus 33 is conditioned to respond to a digit transmitted over the trunk line 81.

At this time, the subscriber at the calling subscriber substation T1 proceeds to dial the second digit of the directory number of the called subscriber substation T3 in the remote exchange 26; whereby the impulses of the second digit are transmitted from the dial 13 at the calling subscriber substation T1 over the previously traced loop circuit, including the link 51 to the line relay RMB in the secondary trunk 1139; whereby the line relay R1 18 follows. The first time the line relay R140 restores it completes, at the contacts 143, a circuit, including the contacts 151, for operating the dial relay R1 F55. Upon operating the dial relay R166 completes, at the contacts 166, a multiple point around the contacts i32 of the detector relay R138, in the previously traced circuit for maintaining operated the test relay R1813. Also the dial relay R169 interrupts, at the contacts 162, the previously traced path for bridging the uppe Winding of the answer relay R120 across the line conductors of the incoming trunk 84; and prepares, at the contacts 153, an alternative dialingbridge traced hereinafter across the line conductors of the incoming trunk 84. Further, the dial relay R150 completes, at the contacts 161, an obvious path for short-circuiting the upper winding of the detector relay R138; and completes, at the contacts 164, an obvious path for short-circuiting the impedance element thereby to improve the dialing circuit extending between the calling subscriber substation T1 and the line relay R146. Finally, the dial relay R160 interrupts, at the contacts 165, a further point in a circuit traced hereinafter for operating the intercept relay R111]. Thereafter each time the line relay R140 restores and then reoperates it interrupts and then recompletes, at the contacts 142, the previously mentioned circuit for maintaining, operated the hold relay R151); whereby the latter relay is retained in its operated position during impulsing since it is of the slow-to-release type. Also each time the line relay R140 restores and then reoperates it completes and then interrupts, at the contacts 1%, the previously traced circuit for maintaining operated the dial relay R; whereby the latter relay is retained in its operated position during impulsing since it is of the sloW-to-release type. Finally each time the line relay R1 50 restores and then reoperates it interrupts and then recompletes, at the contacts 141, the previously mentioned dialing bridge, including the contacts 163, 181, and 152 and the wipers 191 and 192 of the hunt switch 198, across the line conductors of the incoming trunk 8Q; whereby the impulses of the second digit are repeated by the line relay R1 51), at the contacts hi1, over the line conductors of the incoming trunk 8 to the trunr circuit 82; which digit is repeated by the trunk circuit 82 over the trunk line 81 to the switching apparatus 83 in the remote exchange 2i! in order to cause corresponding operation thereof. In passing, it is noted that each time the above traced loop circuit between the line relay R1 18 and the calling subscriber substation T1 is completed at the impulsing springs 14 of the dial 13, that the lower winding of the detector relay R139 is energized; the upper winding of the detector relay R139 being short-circuited at this time; whereby the detector relay R131} operates and restores intermittently. This intermittent operation of the detector relay R138 is without eiiect at this time since the operated dial relay R168 retains interrupted, at the contacts 165, a circuit traced hereinafter for operating the intercept relay R1'10.

At the conclusion of the second digit dialed at the calling subscriber substation T1, the line relay RMU is retained in its operated position, maintaining interrupted, at the contacts 143, the previously traced circuit for maintaining operated the dial relay R; whereby the latter relay restores shortly thereafter, it being of the slow-to-release type. Upon restoring the dial relay RIBU interrupts, at the contacts 161, the previously mentioned path for short-circuiting the upper winding of the detector relay R130; thereby to cause the latter relay to restore since both the upper and lower windings thereof are now energized and it is of the differential type. Also the dial relay R1150 interrupts, at the contacts 164, the previously mentioned path for shortcircuiting the impedance element 135; and interrupts, at the contacts 166, the previously mentioned point in multiple to the contacts 132 of the restored detector relay R130. Also the dial relay R161! reprepares, at the contacts 185, a further point in the previously mentioned circuit for operating the intercept relay R110; and inter rupts, at the contacts I63, the previously traced dialing bridge across the line conductors of the incoming trunk 8 and recompletes, at the contacts I62, the previously traced original loop aircuit including the upper winding of the answer relay RIZO across the line conductor of the incoming trunk 84.

In a similar manner the third and subsequent digits of the directory number of the called sub scriber substation T3 in the remote exchange 20 are dialed at the calling subscriber substation TI in the central office It and repeated by the secondary trunk It"! to the trunk circuit 82, and therefrom over the trunk line 8| to the switching apparatus 83 in the remote exchange 20 in order to bring about operation of the switching apparatus 83 to select the subscriber line 85 extending to the called subscriber substation T3. The subsequent operation of the switching apparatus 83 depends upon the idle or busy condition of the called subscriber substation T3, in a conventional manner; and assuming that the called subscriber substation T3 is idle at this time, when the call is answered thereat, the switching apparatus 83 effects the reversal of polarity over the trunk line BI; whereby the trunk circuit 82 effects reversal of polarity over the incoming trunk 84. When the polarity of the incoming trunk 86 is thus reversed, the upper winding of the answer relay RIZB is poled to operate. Upon operating the answer relay RIZEI reverses, at the contacts I2I, I22, 523, I24, the polarity of the loop circuit extending between the calling substation TI and the line relay RIM; which reversal of polarity over the loop circuit mentioned may be employed for metering purposes in a conventional manner. The established connection between the calling subscriber substation TI in the central oilice I6 and the called subscriber substation T3 in the remote exchange 29 persists for any desired time interval at the convenience of the subscribers at the substations mentioned.

At the conclusion of the connection when the subscriber at the called subscriber substation T3 in the remote exchange 20 replaces the receiver of the elephone instrument thereat upon its associated switchhook, the switching apparatus 83 is controlled in order to bring about the reversal of polarity over the trunk line BI whereby the trunk circuit 82 eiTects the reversal of polarity over the incoming trunk 84, in order to cause the answer relay RIZE! to restore. Upon restoring the answer relay RI2IJ again effects the reversal of polarity, at the contacts I2I, I22, I23, I24, over the loop circuit extending between the calling subscriber substation TI and the line relay RIM When the subscriber at the calling subscriber substation TI in the central ofiice l replaces the receiver of the telephone instrument II thereat upon its associated switchhook, the previously traced loop circuit extending therefrom to the line relay RIM? is interrupted in order to effect the restoration of the line relay RIM. Upon restoring the line relay RIM] interrupts, at the contacts I 42, the previously mentioned circuit for maintaining operated the hold relay RIEQ; whereby the latter relay restores shortly thereafter it being of the slow-to-release type. Upon restoring the hold relay RISt interrupts, at the contacts I52, the previously mentioned path for applying ground potential to the control conductor CH3 of the trunk H0 and the previously traced path for applying ground potential by way of the wiper I93 of the hunt switch I90 to the control conductor of the incoming trunk 84; when ground potential is thus removed from the control conductor CI I3 of the trunk IIII, both the finder '52 and the selector 53 of the link 5| are released; and battery potential by way 'of the lower winding of the answer relay RI20 is ap plied to the control conductor CI I3 of the trunk I Ill; thereby to mark the trunk I It as idle to the selectors of the various links having access thereto. When ground potential is removed from the control conductor of the incoming trunk 84, the trunk circuit 82 is released in order to bring about the release of the switching apparatus 83 connected thereto by the trunk line 8|; whereby the subscriber line 85 extending to the called subscriber substation T3 is again marked as idle to the switching apparatus 83. When the finder 52 of the link 5| is released in the manner explained above, the line circuit 35 individual to the party line 3!! is controlled in order to remove the application of ground potential upon the con"- trol conductor CM thereof and to reapply battery potential to the control conductor C34; whereby the party line 38 is marked as idle to the'connectors GI, etc. in the first group having access thereto. Also when ground potential is removed from the control conductor CI I3 of the trunk III], the previously traced holding circuit for maintaining operated the test relay RIBII, is -in= terrupted, whereby the latter relay restores. At this time, the secondary trunk IEiII is completely released; and all of the apparatus utilized in the established connection between the calling subscriber substation TI the central oflice II) and the calling subscriber substation T3 in the remote exchange 20 is completely released and is avail able for further use.

Now assume that a call has been initiated at the subscriber substation T2 rendered restricted service in the central office Ii]; that the finder 52 of the link 5| has operated to find the party line 30 extending to the subscriber substation T2; that the selector 53 of the link 5! is conditioned to be responsive to the first digit dialed at the calling subscriber substation T2; and that the subscriber at the calling subscriber substation T2 attempts the extension of a connection to a called subscriber substation in the remote eX-,

change 26. The subscriber at the calling sub scriber substation T2 proceeds to dial the first digit of the directory number of the called sub scriber substation in the remote exchange 26 thereby to bring about operation of the selector 53 toselect an idle trunk in the group, including the trunk I It, in the manner previously explained. Assuming that the selector 53 seizes the particular trunk He, the line relay RIM and the hold relay RI50 in the secondary trunk Hill are operated; whereby operation of the hunt switch Itil is initiated; all in the manner previously explained. More particularly, the hunt switch 5% operates to select an idle trunk extending between the central office I0 and the remote exchange 253; and it may be assumed that the hunt switch I select the incoming trunk 84 extending to the trunk circuit 82; whereby the switching apparatus 83 in the remote exchange 26 is controlled over the trunk line 8| in order to be conditioned to be responsive to the second digit of the directory number of the called subscriber substation in the remote exchange 20; all in the manner previously explained. At this time, the test relay RIBD- in the secondary trunk IE0 is operated and the secondary trunk IIIII is conditioned to repeat the second digit of the directory numb er dialed at the calling subscriber substation T2, in the manner previously explained.

However, in the present example, when the subscriber at the calling subscriber substation T2 operates the finger wheel of the dial 23 in preparing it to transmit the second digit of the directory number of the called subscriber substation in the remote exchange 25, the set of off-normal springs 25 therein are actuated into engagement; thereby to cause ground potential to be applied to the line conductors C3I and C32 of the party line, and consequently to the line conductors Ci H and CE I2 of the trunk I I5. This application of ground potential to the line conductor CI II of the trunk Ilfl completes an obvious alternatin circuit for energizing in series the upper winding of the detector relay RI3II and the winding of the line relay R149; while this application of ground potential to the line conductor CI I2 or the trunk I I9 completes an obvious path for short-circuiting in series the lower winding of the detector relay RI35 and the impedance element I35. Accordingly, the upper winding of the detector relay RISE is energized and the lower winding thereof is short-circuited; whereby the detector relay RISG operates since it is of the differential type. Upon operating the detector relay RI39 completes, at the contacts I3I, the previously mentioned circuit, including the contacts I65, for energizing the winding of the intercept relay RIH); whereby the latter relay operates shortly thereafter, it being of the slow-to-operate type. Also upon operating the detector relay RI30 interrupts, at the contacts I32, the previously traced holding circuit for energizing the winding of the test relay RI89 in series with the magnet MI95; thereby to cause the latter relay to restore. Upon restoring the test relay RIM interrupts, at the contacts IBI and I82, the previously traced loop circuit extending between the upper winding of the answer relay RIM and the line conductors of the incoming trunk 84; thereby to efiect the release of the trunk circuit 82 and the consequent release of the switching apparatus 83 in the remote exchange 20. When the intercept relay RI'IIJ operates, as previously noted, it completes, at the contacts I'II, a holding circuit therefor, including the contacts I52; and interrupts, at the contacts I13, a further point in the previously traced path for applying battery potential by way of the magnet MI95 to the wiper 593 of the hunt switch I90. Also the intercept relay RI'IO completes, at the contact I12, a path, including the contacts I84, I53 and I96, for applying battery potential by way of the magnet MI95 to the wiper I94 of the hunt switch -I90; which wiper I94 engages a grounded contact in the associated contact bank by virtue of the position of the wipers noted of the hunt switch I99 at this time. Accordingly, the magnet MI95 operates buzzer-fashion in order to drive the wipers noted of the hunt switch I90 acros the contacts in the associated contact banks terminating the remainder of the incoming trunks extending to trunk circuits terminating trunk lines extending between the central ofice I and the remote exchange 29. When the wiper 94 of the hunt switch I99 is driven to disengage the last ground contact in the associated contact bank and to engage the adjacent contact terminating the control conductor of the first incoming trunk in the group of three trunks extending to the interceptor operator position 95, the incoming trunk mentioned is tested in order to determine the idle or busy condition thereof. Assuming that the first trunk 92 in the group mentioned is idle at this time, battery potential in the trunk circuit 9I connected thereto appear upon the control conductor of the incoming trunk 99; thereby to complete a path substantially identical to that previously traced for short-circuiting the magnet MI95. Accordingly at this time, an alternative circuit, including the contacts I52, I14 and I96, is completed for energizing the winding of the test relay RIBfl in series with the magnet MI95; whereby the test relay RIBIl operates shortly thereafter, it being of the slow-to-operate type. However, the magnet MI95 does not operate due to the high serie resistance of the winding of the test relay RI89. Upon operating the test relay RISE) interrupts, at the contact I84, the previously traced path for applying battery potential by way of the magnet MI95 to the wiper I94; and completes, at the contacts I83 a path, including the contacts I52 and I72, for applying ground potential directly to the wiper I94; further the test relay RISE completes, at the contacts I8I and I82, a loop circuit substantially identical to that previously traced between the upper winding of the answer relay RI20 and the line conductors of the incoming trunk 99 extending to the trunk circuit 9 I. When the hunt switch I99 is thus operated to seize the incoming trunk extending to the trunk circuit 9I, the trunk circuit 9i operates to transmit over the trunk 92 a call signal to the interceptor operator position 95; thereby to indicate to the operator thereat that a call is waitin to be answered on the trunk 92.

Subsequently, when the subscriber at the calling subscriber substation T2 releases the finger wheel of the dial 23, the second digit of the directory number of the called subscriber substation in the remote exchange 29 is transmitted thereby to the line relay RMI]; and repeated by the line relay RIM over the incoming trunk 90 to the trunk circuit 9|; which operations are without effect at this time. During the reception of the impulses of the second digit mentioned, the dial relay R again operates; and at the conclusion of the second digit mentioned, the dial relay RISO restores shortly thereafter, bringing about the restoration of the detector relay RI30. The operator at the interceptor position 95 then answers the call on th trunk 92 completing a loop circuit extending therefrom by way of the trunk 92, the trunk circuit 9i and the incoming trunk 99 to the upper winding of the answer relay RIZIl in the secondary trunk I99; whereby the upper winding on the answer relay RIZB is not poled to operate since the call has been extended to the interceptor operator position 95. Accordingly, at this time, a connection has been completed between the calling subscriber substation T2 and the interceptor operator position 95 in the central ofiice II]; and when the subscriber at the calling subscriber substation T2 completes the dialing of all of the digits of the directory number Of the called subscriber substation in the remote exchange 20, the operator at the interceptor position 95 converses with the subscriber at the calling subscriber substation T2, advising him that he is not permitted to make calls directly to the remote exchange 26 since the subscriber substation T2 is rendered restricted service. The operator at the interceptor position 95 may undertake th extension of the connection to the desired called subscriber substation in the remote exchange 20, or she may ad- 75 vise the subscriber at the calling subscriber substation T2 to dial the regular tollboard, not shown, after releasing the present connection. The release of the established connection between the calling subscriber substation T2 and the interceptor operator position 95 takes place in a conventional manner when the subscriber at the calling subscriber substation T2 replaces the receiver of the telephone instrument 2| thereat upon its associated switchhook.

Conclusions In view of the foregoing, it is apparent that both restricted and non-restricted subscriber substations, whether they are connected to individual or party lines, may selectively control the automatic switching apparatus to complete local calls i in the central office ill. However, only non-restricted subscriber substations, whether they are connected to individual or party lines, may selectively control the automatic switching apparatus to complete trunk calls to subscriber substations in the remote exchange as. Moreover, in the event restricted subscriber substations, whether they are connected to individual or party lines, attempt to control the automatic switching apparatus to complete trunk calls to subscriber substations in th remote exchange 26, the calls thus initiated are intercepted at the interceptor operator position 95 in the central office it].

While there has been described what is at present considered to be the preferred embodiment of the invention, it will be understood that various modifications may be mad therein; and it is intended to cover in the appended claims all such modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. In a telephone system including a first exchange provided with subscriber substations of first and second classes and automatic switching apparatus accessible thereto, each of said subscriber substations being provided with a digit transmitting mechanism, a second exchange, and a plurality of trunks extending between said exchanges and accessible to said switching apparatus; means controllable from any calling one of said subscriber substations for extending a connection therefrom to said switching apparatus, means responsive to the extension of a connection to said switching apparatus for operating it automatically to select an idle one of said trunks, means including a first relay responsive to the transmission of a digit to said switching apparatus from a calling one of said subscriber substations of said first class for repeating the digit over said one selected trunk, and means including a second relay responsive to the transmission of a digit to said switching apparatus from a calling one of said subscriber substations of said'se'cond class for reoperating said switching apparatus to release said one selected trunk.

2. In a telephone system including a first exchange provided with subscriber substations of first and second classes and automatic switching apparatus accessible thereto and an operator position accessible to said switching apparatus, each of said subscriber substations being provided with a digit transmitting mechanism, a second exchange, and a plurality of trunks extending between said exchanges and accessible to said switching apparatus; means controllable from any calling one of said subscriber substations for extending a connection therefrom to said switching apparatus, means responsive'to the extension of a connection to said switching apparatus for operating it automatically to select an idle one of said trunks, means including a first relay responsive to the transmission of a digit to said switching apparatus from a calling one of said subscriber substations of said first class for repeating the digit over said one selected trunk, and means including a second relay responsive to the transmission of a digit to said switching apparatus from a calling one of said subscriber substations of said second class for reoperating said switching apparatus to release said one selected trunk and to extend the connection to said operator position.

3. In a telephone system including a first exchange provided with subscriber lines extending to subscriber substations of first and second classes and automatic switching apparatus accessible to said subscriber lines, a second exchange, and a plurality of trunks extending between said exchanges and accessible to said switching apparatus, each 01" said subscriber substations of said first class being provided with a conventional impulse transmitting mechanism selectively operable to transmit impulses over the connected subscriber line, each of said subscriber substations or said second class being provided with a unique impulsing transmitting mechanism selectively operable to transmit impulses over and to apply a special signal to the connected subscriber line; means controllable from any calling one of subscriber substations for extending a connection therefrom via the connected subscriber line to said switching apparatus, means responsive to the extension of a connection to said switching apparatus for operating it automatically to select an idle one of said trunks, means including a first relay normally responsive to the transmission of impulses over a subscriber line connected to said switching apparatus for repeating corresponding impulses over said one selected trunk and means including a second relay responsive to the application of said special signal to a subscriber line connected to said switching apparatus for reoperating said switching apparatus to release said one selected trunk.

4. In atelephone system including a first exchange provided With subscriber substations of first and second classes and automatic switching apparatus accessible thereto, a second exchange, and a plurality of trunks extending between said exchanges and accessible to said switching apparatus, each of said subscriber substations of said first class being provided with a conventional digit transmitting mechanism selectively operable to transmit any desired digit, each of said subscriber substations of said second class being provided with a unique digit transmitting mechanism selectively operable to transmit any desired digit and also to transmit therewith a special signal; means controllable from any calling one of said subscriber substations for extending a connection therefrom to said switching apparatus, means responsive to the extension of a connection to said switching apparatus for operating it automatically to select an idle one of said trunks, means including a first relay normally responsive to the transmission of a digit to said switching apparatus for repeating the digit over said one selected trunk, and means including a second relay responsive'to the transmission of said special signal to said switching apparatus for reoperating said switching apparatus to release said one selected trunk.

5. In a telephone system including a first exchange-provided with party subscriber lines extending to party subscriber substations of first and second classes and automatic switching apparatus accessible to said party subscriber lines, a second exchange, and a plurality of trunks ex tending between said exchanges and accessible to said switching apparatus, each of said party subscriber substations of said first class being provided with a conventional impulse transmitting mechanism selectively operable to transmit impulses over the connected party subscriber line, each of said party subscriber substations of said second class being provided with a unique impulsing transmitting mechanism selectively operable to transmit impulses over and to apply a special signal to the connected party subscriber line; means controllable from any calling one of said party subscriber substations for extending a connection therefrom via the connected party subscriber line to said switching apparatus, means responsive to the extension of a connection to said switching apparatus for operating it automatically to select an idle one of said trunks, means including a first relay normally responsive to the transmission of impulses over a party subscriber line connected to said switching apparatus for repeating corresponding impulses over said one selected trunk, and means including a second relay responsive to the application of said special signal to a party subscriber line connected to said switching apparatus for reoperating said switching apparatus to release said one selected trunk.

6. In a telephone system including a first exchange provided with a party line serving subscriber substations of first and second classes and automatic switching apparatus accessible to said party line, each of said subscriber substations being provided with a digit transmitting mechanism, a second exchange, and a plurality of trunks extending between said exchanges and accessible to said switching apparatus; means controllable from any calling one of. said subscriber substations for extending a connection therefrom over said party line to said switching apparatus, means responsive to the extension of a connection to said switching apparatus for operating it automatically to select an idle one of said trunks, means including a first relay responsive to the transmission of a digit to said switching apparatus from a calling one of said subscriber substations of said first class for repeating the digit over said one selected trunk, and means including a second relay responsive to the transmission of a digit to said switching apparatus from a calling one of said subscriber substations of said second class for reoperating said switching apparatus to release said one selected trunk.

'7. In a telephone system including a first exchange provided with a party line serving subscriber substations of first and second classes and automatic switching apparatus accessible to said party line and an operator position accessible to said switching apparatus, each of said subscriber substations being provided with a digit iii) transmitting mechanism, a second exchange, and a plurality of trunks extending between said exchanges and accessible to said switching apparatus; means controllable from any calling one of said subscriber substations for extending a connection therefrom over said party line to said switching apparatus, means responsive to the extension of a connection to said switching apparatus for operating it automatically to select an idle one of said trunks, means including a first relay responsive to the transmission of a digit to said switching apparatus from a calling one of said subscriber substations of said first class for repeating the digit over said one selected trunk, and means including a second relay responsive to the transmission of a digit to said switching apparatus from a calling one of said subscriber substations of said second class for reoperating said switching apparatus to release said one selected trunk.

8. In a telephone system including a first exchange provided with a party line serving subscriber substations of first and second classes and automatic switching apparatus accessible to said party line, a second exchange, and a plurality of trunks extending between said exchanges and accessible to said switching apparatus, each of said subscriber substations of said first class being provided with a conventional digit transmitting mechanism selectively operable to transmit any desired digit, each of said subscriber substations of said second class being provided with a unique digit transmitting mechanism selectively operable to transmit any desired digit and also to transmit therewith a special signal; means controllable from any calling one of said subscriber substations for extending a connection therefrom over said party line to said switching apparatus, means responsive to the extension of a connection to said switching apparatus for operating it automatically to select an idle one of said trunks, means including a first relay normally responsive to the transmission of a digit to said switching apparatus for repeating the digit over said one selected trunk, and means including a second relay responsive to the transmission of said special signal to said switching apparatus for reoperating said switching apparatus to release said one selected trunk.

JOHN WICKS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,256,126 Goodrum Feb. 12, 1918 1,649,494 Smith Nov. 15, 1927 2,039,668 Stokely May 5, 1936 2,214,213 Voss Sept. 10, 1940 2,217,041 Boswau Oct. 8, 1940 2,248,575 Lomax July 8, 1941 2,286,431 Molnar et al. June 16, 1942 2,299,514 Taylor Oct. 20, 1942 2,366,647 Ostline Jan. 2, 1945 

